libde265 is a robust, LGPL-licensed C library implementing the H.265/HEVC video codec standard. It provides a full decoder (Main profile with range extensions) and an experimental encoder. The library is designed for integration into media software (e.g., libheif, GStreamer, VLC) and includes a clean C API (de265.h) for decoding and a similar API for encoding. Internally, it features a modular architecture with SIMD acceleration for x86 (SSE4.1, AVX2, AVX512) and ARM (NEON), a branchless CABAC decoder, multi-threading via WPP and tiles, and a function-pointer-based acceleration abstraction. Example applications include a command-line decoder (dec265), encoder (enc265), and a Qt-based visual debugger (sherlock265). The codebase is actively maintained with CI/CD, fuzzing, and conformance testing, though the encoder remains experimental with incomplete features. The library is production-grade for decoding and has been battle-tested by downstream projects.